This invention relates to magnetic stimulation techniques, and more particularly to neural stimulation using a magnetic field.
Repetitive transcranial magnetic stimulation (rTMS) has been used with the goal of treating depression, see, e.g., George et al., The Journal of Neuropsychiatry and Clinical Neurosciences, 8:373, 1996; Kolbinger et al., Human Psychopharmacology, 10:305, 1995.
One example of an rTMS technique uses a figure-8 surface coil with loops that are 4 cm in diameter (Cadwell, Kennewick, Wash.). This coil is placed next to the scalp, and is usually positioned to direct the magnetic field at the prefrontal cortex of the brain, see, e.g., George et al., The Journal of Neuropsychiatry and Clinical Neurosciences, 8:373, 1996. An electric current is run through the magnetic coil to generate a magnetic field, specifically a sequence of single-cycle sinusoidal pulses where each pulse has a frequency of approximately 1800 Hz (or about 560 microseconds per pulse). These pulses are delivered at a repetition rate of 1 to 20 Hz (i.e., one pulse every 0.05 to 1 second), see, e.g., George et al, Biological Psychiatry, 48:962, 2000; Eschweiler et al, Psychiatry Research: Neuroimaging Section, 99:161, 2000.
Some subjects have declined participation in rTMS studies due to pain induced in the scalp. In addition, seizures have been reported as a result of rTMS treatment, see, George et al, Biological Psychiatry, 48:962, 2000; Wasserman, Electroencephalography and Clinical Neurophysiology 108:1, 1998.
The invention concerns enhancing brain function using novel magnetic field techniques. These magnetic field techniques use low field strengths, high repetition rates, and uniform gradients to improve brain function.
In one aspect of the present invention, a subject is selected for enhancement of brain function using a magnetic field. The subject""s head is then subjected to a time-varying magnetic field having a maximum strength of less than about 50 G.
Advantages of this aspect of the invention include the following. Subjects with cognitive impairments may benefit from the new treatment by the lessening of the severity of the condition. Treatment techniques using this method can be administered inexpensively with relative safety and comfort, and offer a substitute for or complement to treatment by medication. Applications of the new methods include improving the condition of individuals with cognitive disorders, such as depression, and studying the effects of brain stimulation using induced electric fields.
Embodiments of this aspect of the invention can include one or more of the following features. After treating the subject (e.g., a human patient), the subject can be evaluated for enhanced brain function. The magnetic field can have a maximum strength of less than about 10 G. The field can also be a gradient magnetic field that is substantially uniform (i.e., a magnetic field one or more of whose x, y, or z direction components varies approximately linearly in space; that is, has a constant gradient to within, e.g., 10%) and unidirectional over the relevant volume (e.g., the entire brain, or a region of interest of the brain such as the prefrontal cortex). The gradient of the magnetic field can be less than about 5 G/cm. The magnetic field can be generated using a sequence of trapezoidal pulses of alternating polarity, where each pulse has a duration of about 1 millisecond.
In another aspect of the present invention, a subject is selected for enhancement of brain function using a magnetic field. The subject""s head is then subjected to a time-varying gradient magnetic field that is substantially uniform and unidirectional.
In another aspect of the present invention, a subject is selected for enhancement of brain function using a magnetic field. The subject""s head is then subjected to a time-varying magnetic field generating by a sequence of pulses, each having a duration of less than about 10 milliseconds.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.